Boston Marathon bombing suspect Dzhokhar Tsarnaev is shown in this photo released by the FBI in 2013. / AP

by Michael Winter, USA TODAY

by Michael Winter, USA TODAY

Lawyers for accused Boston Marathon bombing suspect Dzhokhar Tsarnaev asked a federal judge Wednesday to prevent prosecutors from arguing for the death penalty simply because a crowded athletic event was targeted.

They also want Judge George O'Toole to declare the death penalty unconstitutional, in part because of the recent botched executions in Oklahoma and Ohio.

Tsarnaev's lawyers argued that because prosecutors already claim the 2013 attack was an act of terrorism that followed extensive planning, the jury should not consider the death penalty just because the race was the target.

"Stated differently, the allegation that Tsarnaev targeted the marathon is simply a more specific statement of the substantial planning allegation," the lawyers wrote in a court filing. Therefore, jurors should not consider it an "aggravating factor" in any sentencing deliberations.

Last week, the defense moved to strike another aggravating factor cited by the U.S. attorney - the alleged betrayal of the United States by the naturalized citizen. They said having duplicative aggravating factors "can have no other effect than to introduce arbitrariness and unfairness into the jury's sentencing deliberations."

Tsarnaev, 20, is awaiting trial on 30 counts related to the bombing, 17 of which are eligible for the death penalty.

He and his 26-year-old brother, Tamerlan, allegedly planted two pressure-cooker bombs that exploded near the finish line, killing three and injuring more than 260. Tamerlan Tsarnaev died days later after a shootout with police.

In asking O'Toole to strike down the death penalty, the lawyers said the U.S. Constitution's ban on cruel and unusual punishment should apply, because Massachusetts does not allow capital punishment.

They also said it has been proven that innocent people have been executed in recent years, and that there has been "worldwide revulsion over the recurring spectacle of botched executions," including last week's botched lethal injection of Oklahoma murderer Clayton Lockett. He died of a heart attack 40 minutes after the execution began.

In January, an Ohio inmate took 26 minutes to die.

The lawyers did note one possible hurdle they face: a U.S. appellate court rejected a challenge to the federal death penalty in another Massachusetts case in 2007.